The present invention relates to a doctor for a suction roll particularly in paper machines, which doctor is intended to remove water from the suction roll, and which doctor includes a doctor slat arranged against the surface of the suction roll and essentially extending over the entire length of the suction roll, together with the doctor slat""s retaining and loading members.
A suction roll doctor, which removes water from the suction roll, is known from FI patent application number 902910. The blade used in the doctor is a doctor slat, which scrapes the film of water off the surface of the suction roll. In addition, the doctor slat creates a suction zone behind itself, which also removes the water that has collected in the drill holes and grooves of the suction roll. Part of the water raised by as the suction flows into a drainage tank beneath the suction roll, but the rotation of the suction roll causes part of the moisture to travel back into the felt or similar. This causes the web or felt to become soaked, or at least causes unevenness in the moisture profile of the web, felt, or paper.
A double doctor, in which an attempt has been made to improve the water removal capacity of the doctor by using two doctor blades, has also been manufactured for similar use. However, a conventional doctor blade cannot be used to achieve the suction effect of a doctor slat according to the invention, which can also suck the water out of the holes of the suction roll. In addition, doctor blades operate in the desired manner only over a certain part of the circumferential speed range of the suction roll. In this case, when the speed of the paper machine increases, both the water removal capacity of the doctor in question and the result of the doctoring diminish substantially.
The invention is intended to create a new kind of doctor for a suction roll particularly in paper machines, by means of which water can be removed from the suction roll more effectively than previously.
A doctor for removing water from a suction roll in a paper machine includes a doctor slat fitted against the surface of the suction roll extending essentially over the entire width of the suction roll, as well as its holder and loading devices. In the direction of the rotation of the suction roll, there is a doctor blade and a blade holder fitted to the doctor after the doctor slat and arranged to remove the water lifted off the suction roll by the doctor slat. The angle between the lines of contact of the doctor slat and the doctor blade in relation to the imagined axis of rotation of the suction roll is 15-70xc2x0, preferably 20-40xc2x0.
The doctor has a frame construction, to which holders of both the doctor slat and the doctor blade are fitted. The holder of the doctor slat is fitted detachably to the frame construction. The frame construction includes attachments corresponding to the blade holder of the doctor blade in the vicinity of the holder of the doctor slat.
The combination construction of a doctor according to the invention actualizes the advantageous properties of the doctor, in practice creating an excellent doctoring result. Simultaneously, a significant increase in the total solids content is achieved. Besides water, fibres and filler substances are also removed from the holes in the suction roll. This reduces the amount of loose material rotating with the suction roll and also helps the suction roll""s holes to remain clean. The doctor also evens the humidity in the area around the suction roll, as most of the water is recovered in a controlled manner. Thus, the web, felt, or similar do not become soaked, instead an even moisture profile is maintained. A doctor according to the invention can be used in all suction roll positions. In addition, only small alterations are required to adapt the doctor to a very broad area of the auction roll""s speed range.
In the following, the invention is described in detail with reference to the accompanying drawings, depicting some embodiments of the invention, in which drawings